@bigbadmomma45,
"I found it odd that USPS marked delivered on Saturday but buyer claim the product arrived on Tuesday".
Not odd at all since it was a holiday weekend. The buyer may have been away and returned Mon. night, then didn't look for the package until Tues.
"I accidentally accepted the return on my mobile device, which I did not intend to do!!"
I do not use ebay's app at all, and only use my phone to search occassionally on eBay. Because it is too easy for my big clumsy fingers to accidentally touch the wrong thing on a screen, I would never log into my selling account on a portable device. Because you accidentally accepted the return you are now committed to follow through.
"What can be done so that I can get my money for my item that has been confirmed delivered but alledgedly missing parts and also refund her the money"?
There is really nothing you can do to get money for a "damaged opened package" unless you bought insurance or used Prioriy mail, which has an automatic $50 insurance. Had the package been delivered that way, there should have been a damaged package notice. Even if you had insured the package refunding the buyer is not dependent on the outcome of a postal insurance claim. You refund the buyer first then deal with the USPS.
"She's willing to close the damaged missing parts case for a reasonable solution".
How I would proceed, would depend on what her feedback left for other sellers looked like. Do many of their positive comments mention problems, or say things like "seller worked with me", "quick refund given"? Are there many nit-picky neutral feedback or negatives calling sellers scammers thieves etc.? If there are then it is likely this person uses the Money Back Guarantee (MBG) to get full or partial refunds often. All you can do with a buyer like that is to give a refund, block them, and then report them for possible abuse of the MBG.
Since you are now required to send a shipping label for returning the package, even though it might take a smaller box and be lighter to return. If you decide to ask for the remaining items back, to give a full refund, ask them to return the original box and remaining items. If it looks like the buyer likes to leave negatives, offer a partial refund, cut your losses and possibly avoid a non positive feedback.
"THERE IS NO SUCH THING AS FOOLPROOF, BECAUSE FOOLS ARE SO DARNED INGENIOUS!" (unknown)
